Many existing commutators, high-speed rotary switches typically used with electric motors, comprise multiple copper segments arranged into a cylinder and anchored into a non-conducting (often phenolic) molding compound. Each segment is physically separated and electrically isolated from those adjacent to it, so that an electrical brush passing along the outer diameter of the cylinder will form a conductive path only with the segment (or segments) in contact with it at any given instant. With one electrical brush, therefore, for each rotation of the cylindrical commutator the number of possible state changes is equal to twice the number of its copper segments.
These existing commutators are formed in various manners. One such method, producing a "built-up" product, requires formation of each conducting segment individually. The individual segments are then arranged circularly in a frame. After the segments are properly placed, a molding compound is inserted into the central area of the frame in contact with the inner surfaces of each segment.
Another formation method produces a cylindrical shell by curling a flat copper strip. As with the "built-up" method, molding compound is then inserted into the center of the cylindrical structure to create the core of the finished product. Thereafter the individual conducting segments are formed by cutting, or slotting, periodically through the copper cylinder. The widths of these slots space each segment from those adjacent to it, providing the electrical isolation necessary for proper operation of the commutator. Although less expensive to manufacture, existing shell commutators are often less durable than their "built-up" counterparts.
Both shell and "built-up" commutators operate at high speeds, approaching, in some cases, many thousands of revolutions per minute. As a result, the conducting segments are subjected to substantial centrifugal and thermal forces, tending ultimately to disengage the segments from the central core and thereby cause the commutators to fail. Currently-existing manufacturing processes, therefore, can be manipulated to form interior features for the segments which act to anchor the segments into the molded core. Features presently in use by various manufacturers resemble, for example, dovetail-shaped recesses, acute angular protrusions, and hooks. The hooks and acute angular protrusions are created, usually in pairs, by free-form paring the interior surfaces of the segments.
The molding compound is also exposed to the centrifugal and thermal forces during operation, which in some cases can reduce the useful life of the commutator by destroying the integrity of the molding compound itself. This potential problem can be particularly acute if the integrity of the compound is disturbed near the anchors of any particular segment. As a result, a need exists to reinforce the compound and remainder of the commutator and protect against these adverse consequences.